We also investigated the HHG spectra dependence versus pump wave frequency
and intensity. In Figs. 4(a) and 4(b) we plot the HHG spectra versus pump
wave frequency at moderate EEI energy \(U=2\)  \(\mathrm {eV}\) , for C\(_{60}\)  and C\(_{70}\) , respectively. For both molecules, the cutoff harmonic position is
well approximated by the dependence \(N_{\mathrm {cut}}\sim \omega ^{-1/2}\) 
which is plotted along with density plot. Note that for atomic HHG via free
continuum \(N_{\mathrm {cut}}\sim \omega ^{-3}\)  [1]}. In case of
two-level atom \(N_{\mathrm {cut}}\sim \omega ^{-1}\)  [2]}. Thus, in
contrast to atomic cases for fullerene molecule with the increase of the
pump wave photon energy the cutoff harmonic energy (\(\hbar \omega N_{\mathrm {cut}}\) ) is increased.
